<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var count = 0;
        //1~5
        var index = 20;
        while(index<=80){
            if(index % 2 === 1){
                count += index;//count = count + index;
            }
            index++
        }
        console.log(count);
    </script>
</body>
</html>